The elicitation of potent and broad anti-HIV-1 neutralizing antibodies (NAbs) by immunization has been one of the major goals of HIV research since the beginning of the HIV/AIDS epidemic. So far, this goal has not been attained. The target of anti-HIV-1 NAbs is the viral envelope glycoprotein (Env) and several forms of HIV Env have been tested as immunogens over the past three decades. The lack of elicitation of antibodies with broad neutralizing activities by soluble Env immunogens is not due to the absence of relevant epitopes on such constructs. Understanding why conserved neutralization epitopes are poorly immunogenic during immunization by HIV Env constructs is the focus of this proposal. Our overall hypothesis is that the biophysical characteristics of the epitope-BCR interaction, especially the kon and koff binding rates of that interaction, dictate the downstream intracellular events that lead to either B cell-differentiation and antibody production, or to B cell-anergy. To test this hypothesis we propose a series of iterative studies that will improve our understanding of the structural and biophysical characteristics of immunogen-BCR interactions and of how these interactions influence downstream events that lead to B cell activation or anergy. Our team is composed of groups with diverse expertise that have a documented record of collaboration. Dr. Schief's group at the University of Washington is leading our immunogen-design efforts. Dr. Strong's group at the Fred Hutchinson Cancer Research Center is leading our efforts to characterize the structure of immunogens and the antibodies they elicit and their biophysical interactions. Dr. Stamatatos' group is leading our efforts to analyze the interaction of our immunogens with B cells. We are supported in our efforts by Dr. Atchison's group at the Institute for Systems Biology who will define those intracellular events that lead to optimal B cell stimulation and those that lead to B cell anergy or apoptosis, following the binding of b12 scaffolds on the BCR on B cells.